In a large saucepan, bring water and bouillon to a boil. Add broccoli. Reduce heat; cover and simmer for 3-4 minutes or until crisp-tender. Drain, reserving 3/4 cup liquid. In another large saucepan, saute onion in butter until tender. Whisk in flour until blended. Add the milk and cheese. Cook over medium-low heat until cheese is melted, stirring frequently. Stir in broccoli and reserved cooking liquid.